To      :Sarah B.
Re      : Thallium Scanning

201 Thallous Chloride is used most commonly for myocardial perfusion
imaging.  After IV administration nearly 85% is extracted by the myocytes
during first pass of the isotope by the heart.

The half-life of the isotope is rather long at  73 hours. The whole body
biological half-life is about 10 days,  but the radioactivity would be
largely gone by this time.  In this case,  the thallium ion stays in the
body longer than the product is radioactive.  But the absolute dose of
thallium would be incredibly low, so the risk of thallium poisoning is nil.

We do not know how much if any thallium transfers into human milk.  I would
assume it to be low.  In this case, to be 'absolutely' safe, one would need
to pump and dump for 4-5 radioactive half-lives (about 12 days).

Newer isotopes are being investigated to replace Thallium and include:
99m Tc-Sestamibi
99m Tc-Teboroxime

Regards

Tom Hale, Ph.D.